The field of the invention is shaped, hollow sections, in particular tubes, which are made from polyamides and used as supply lines for the fuels of internal combustion engines.
These polyamides have as the fundamental unit (repeating unit) lactams or omega-amino-carboxylic-acids having at least five carbon atoms per carbon amide group, such as nylon-6, nylon-8, nylon-11, or nylon-12, or polyamides from equivalent quantities of aliphatic dicarboxylic acids and aliphatic diamines which together have at least 12 carbon atoms, for instance nylon-6-6, nylon-6-8, nylon-6-9, nylon-6-10, and nylon-6-12.
It has been found that fuel lines made from these polyamides undergo a longitudinal expansion due to the action from fuels, used for internal combustion engines, in particular with the use of fuels containing alcohols and consisting of alcohols. This longitudinal expansion can be of the order of a few percent. Due to this longitudinal expansion, the lines sag in between the supports, and, accordingly, must be viewed as a source of danger due to rupture and fires resulting therefrom.
The state of the art of extruding tubing and pipe from polyamide plastics may be ascertained by reference to the Kirk-Othmer "Encyclopedia of Chemical Technology," 2nd Edition, Volume 16, (1968), under the section "Polyamide (Plastics)," pages 88-105, particularly pages 89 and 92--nylon-6, nylon-6-6, polylauryl-lactam (nylon-12), polyundecanamide (nylon-11), and additives, and page 99--pipe and tubing extrusion, the disclosures of which are incorporated herein.